Garden Guru: Mother Nature's untrained children will take over

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A wall of Japanese knotweed grows uncontrolled along a railroad right of way on Chesterfield Avenue in Kanawha City.

The jointed red stems of Japanese knotweed make some think it is related to bamboo.

A young empress tree towers over its roadside neighbors.

Tree of heaven rises above a tangle of Japanese knotweed.

CHARLESTON, W.Va. -- I've received some concerns from other gardeners about a big problem, and I must admit that I have the same concerns. So, I'm just going to flat-out ask you. Do you have problem weeds in your garden?A while back, I discussed ways to reduce the weeds in your garden. Now, when we talk weeds, many sources say "a weed is a plant out of place not intentionally sown, whose undesirable qualities outweigh its good points."Some gardeners are adamant weed warriors, using any means to keep the leafy intruders out of their lawns and gardens. Other gardeners have a more relaxed attitude. "At least it's green!" some gardeners exclaim, while others praise the edible qualities of some weeds such as nettles and dandelions. "A dandelion's worst enemy," says my TV friend John Marra, "is an Italian with a knife." (He speaks from experience.)I'm not talking about your run-of-the-mill weeds though. I'm talking about hard-to-control, noxious, downright nasty weeds. These are Mother Nature's untrained children run amok.

We've grown accustomed to some of our old stand-by noxious weeds such as multiflora rose and kudzu. But there are newer, more noxious weeds that could be living right under your nose. The best advice I can give is to catch the problems early, before they escalate out of proportion. Cut them down; remove them; kill them out.The following noxious plants will, in fact, take over your yard in no time flat, refuse to be killed out by most means, and grow faster than you can even imagine. The following three plants are on the top of my enemies list. These plants are not your friends. You have been warned.Japanese knotweedJapanese knotweed (Fallopia japonica) has quickly become an enemy to many gardeners. It has hollow, jointed stems much like bamboo, but is in the Polygonaceae family with rhubarb rather than a grass like bamboo. It can grow up to 12 feet tall, though here it usually grows in the 4- to 6-foot range. It spreads through underground rhizomes, which makes it difficult to eradicate. Pulling it up just seems to propagate new plants -- just like the heads of the Hydra in Greek mythology. Keeping it mowed down can weaken the plant, but complete control through mowing would require years of consistent mowing. Applying a glyphosate herbicide to post-mowing new growth in the fall offers the most consistent control. Even then it might take a few rounds of fighting to knock this pesky plant out.

Empress treePaulownia tomentosa has a way of seducing gardeners into giving it a home and even treating it like it belongs in the landscape. Unwitting gardeners will be surprised that what they think is a giant sunflower with giant leaves starts growing again the next year. The tree grows as much as 8 to 10 feet per year and can go from seed to mature, blooming tree in just a few years. The blooms are huge, purple and pretty, which is why you can still buy these plants in certain garden catalogs.But those blooms give way to prickly, messy seedpods full of seeds bent on domination. They find maintained lawns and gardens an excellent place to set up shop. It amazes me to drive through the area and see people treating these beautiful monsters like they belong in the landscape, with careful pruning and care just like other trees. These trees spread to choke out native trees and plants, though, so they earn a spot on my enemies list.Tree of heavenAnother noxious tree with a cute name, tree of heaven (Ailanthus altissima) is an opportunistic species that outcompetes native trees and fills in forest canopies faster than other trees can grow. Its name comes from the fact that it does reach for the heavens so quickly. It resembles sumacs and other trees, so folks might not know that they have an enemy in their midst. This tree propagates both by seeds and by roots.Its secret weapon is ailanthone, an allelopathic compound that it releases from its roots to kill any competition that finds its way into the root zone, much like black walnuts do. Its roots can also find their way into cracked sewer and water lines.This tree does, however, have a good side (when it is not in your yard or forest): It grows well where other plants do not, such as acid mine drainage fields and mine sites. It tolerates shockingly low pH levels, absorbs sulfur dioxide through its leaves, resists cement dust and coal tar fumes, can live in high-salt and low-fertility soils, withstands drought and will suck up mercury from the soil. In other words, it is a survivor. When the world ends, there will be only cockroaches and Ailanthus altissima.

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I will be giving workshops at the upcoming Mountain State Art & Craft Fair in Ripley on how to grow more food (and in less space) to save time and money. I will present "Making the Most of Your Garden Space" at 1:30 and 3:30 p.m. July 5 and 10 a.m. and 2 p.m. July 6.John Porter is the WVU Extension Service agent for agriculture and natural resources in Kanawha County. He may be reached at john.porter@mail.wvu.edu or at 304-720-9573. Twitter: @WVUgardenguru.